There was a discussion at the office this week concerning the location of a tree on or near a property line. The tree in question is a real sore point with a property owner. Did the party chief say left instead of right, or did the instrument man select left instead of right in the data collector? I explained that if I have any doubt I immediately stake out the point I just located. One of the registered surveyors explained that he always took a shot in front of an object, which would always be recorded as a plus distance. What measures do you take to prevent erroneous offsets?
take field notes
the few extra moments will give you the time to correctly record what you measured
I measure to a side, sight to the middle.There's no room for in out, left right.
I do use the other routine but prefer where possible first option.Staking point is an excellent check.
If it's critical measure to both sides as is. No adjustment, pure measurement.?ÿ
What measures do you take to prevent erroneous offsets?
If I know that the object's location is critical I'll figure out a way to get a redundant measurement.?ÿ But for day-to-day topo (trees, building corners, utility poles, etc.) I rely on experience, knowing that I'll probably screw up one out of every couple hundred offset shots.?ÿ Fortunately, I think I catch a good percentage of bad R/L offsets, because my most frequent goof is not pressing the decimal point key hard enough so that the offset recorded is unreasonably large (e.g., 18 feet instead of 1.8 feet).
I run robotic with the DC on the right side of the prism pole, so most of my R/L offsets are L due to the smaller offset distance.?ÿ Knowing that can be helpful when looking at a suspicious shot, but it's not conclusive.?ÿ Sometimes I can tell if a R/L offset is plausible by looking at the line of sight on the map -- if a right offset would have been blocked by an object, that pretty much settles it as a left offset.?ÿ (I rarely do in/out offsets because it's hard to determine line accurately.)
"remote sideshot" = to locate an object that can not be seen
The most common reason an offset right or left is made is because the object lies behind something and can not be seen from the instrument.
My data collector has the symb0ls: arrow left, arrow up, arrow down and arrow right and the corresponding one that matches the direction from the prism in respect to the viewpoint of the IMan is correct.
Drawings in the fieldbook and pictures are ever so valuable.
The most common reason an offset right or left is made is because the object lies behind something and can not be seen from the instrument.
In robotic work the reason is almost always because the point can't be occupied by the prism, e.g. a building corner or a tree.?ÿ Unless you're using a DC that shows live video from the gun, there's no way to tell the instrument where to point for a "shoot big tree" (old TDS-speak) shot.
I shoot a topo shot at the rod location first and note it in the description- then shoot the offset shot and note the offset in the description- for trees and poles, I shoot the the first topo shot on the face using reflectorless and note it in the description- then I shoot the offset shot reflectorless and note it in the description .
If I am working with another person I have them call it back, if I am working alone I talk to myself. If it is a big tree of clear concern on prop line I may take three shots RL for a three point circle.
Tree location along the perimeter gets a little more TLC than elsewhere.?ÿ
For smaller residential lots I may also set liners straddling the tree which would remove any doubt and aid in fencing.
90 degrees from tree to instrument man for distance record, then angle to center of tree.
Using SurvCE, I measure then take and record my offset. I then press alt+F which instantly turns off all points, except the last stored point, on the DC screen. As long as my Leica TS12 is locked (not in tracking mode) I can see a solid black line referencing the direction the robot is pointing. Then I just check to see if the object was correctly offset based on the orientation of the reference line and the scale displayed on the screen. Offset in or out can be checked in tracking mode or a quick stakeout works too.?ÿ
My method is the use the reflector-less mode. Then measure to three point on the stem of the tree at the standard height and code to make a circle. When the data is downloaded I have the approximate center and diameter of the tree.
We will generally use a two-shot combination. Some of my data collectors have the ability like SMI had using the SDA button. The ones that don't we take two shots and store them both. One for angle and one for distance.
I put it in my description, such as "1' rt to tree"
Typically if I can't occupy something like a tree or pole and I'm going to offset it I'll give the descriptor an "RP_"whatever"_(NSEW) and book the distance. If I want it tight I'll do it twice from 90* and DD Intx. By noting the quadrant or Cardinal direction, pretty much eliminate any possible confusion later.
Every data collector program has some form of distance and/or angle offset routine for shooting such things. If I'm not sure that I got the offset direction right I'll stake out the tree after tying it.
But if the tree, pole, or what-have-you is in a critical location, like right on a boundary, I'm going to reflectorless shoot 3 or more points on its surface and then draw in a 3 point circle using those points back at the office.?ÿ ?ÿField book sketch the points to make sure I've got it.?ÿ ?ÿ
